Weather: The very model of a global argument

After listening to all the arguments of both sides in the global warming debate, one cannot avoid the conclusion that nobody can really be sure about the state of the earth's health.

Let's sort out this global warming thing, shall we? It's perfectly simple: when we burn fossil fuels, it expels carbon dioxide into the atmosphere. And carbon dioxide is one of the greenhouse gases which prevent heat escaping. So the more carbon dioxide is up there, the hotter we become.

That's all very well, but doesn't the carbon dioxide also stop the sun's rays reaching us, thereby cooling us down?

That's what we thought 25 years ago when we worried about an impending ice age. But now we know that the greenhouse heating-up effect is greater than the so-called volcano effect that cools us.

How do we know that?

We've been monitoring the CO2 levels in the atmosphere and there's not much doubt that they correlate with rising temperature.

You mean that the temperature's been going up and the CO2 has been rising, and you suspect a causal connection.

It's far more than that. The claim that we're at the end of a small ice age, and the earth's warming up anyway, and CO2 emissions have nothing to do with it, simply cannot be sustained - the correlations between temperature and gas emissions are too precise for that. Anyway, our computer models of the behaviour of the atmosphere offer an excellent simulation of what has been going on.

Do the predictions of global catastrophe come from the same computer models?

They sure do.

But to predict catastrophe, you must be extrapolating way beyond the range for which the computer models have been verified.

Look, if - to simplify the matter - you have a linear correlation between two quantities between a given range, then by the laws of physics you can expect it to continue linearly for some way beyond that range.

But it's not linear, is it?

No. I was just giving an example to simplify it.

What about Mount Pinatubo? Didn't I read that its eruption cause a drop in world temperature of about 0.2C, which is equivalent to most of the man-made global warming over the past century?

So what?

Well what if global warming led to more volcanic eruptions which could more than cancel out the bad effects?

That's pure speculation. We don't know enough about volcanoes to be able to say anything of the sort.

And what about the algae that consume atmospheric CO2 and sink it to the bottom of the sea. Isn't there some evidence that they are becoming more numerous and helping maintain a balance?

Tricky chaps, algae. We don't know much about them either.

So neither algae nor volcanoes feature in your mathematical models?

Some models have attempted to incorporate them, but they are unreliable. When our current models do the job so well, why make them more complex?